The influence of crystallinity of the hydroxyapatite coating on the fixation of implants

Abstract

We inserted two hydroxyapatite (HA)-coated implants with crystallinities of either 50% (HA-50%) or 75% (HA-75%) bilaterally into the medial femoral condyles of the knees of 16 dogs. The implants were allocated to two groups with implantation periods of 16 and 32 weeks. They were weight-bearing and subjected to controlled micromovement of 250 microm during each gait cycle. After 16 weeks, mechanical fixation of the HA-50% implants was increased threefold as compared with the HA-75% implants. After 32 weeks there was no difference between HA-50% and HA-75%. Fixation of HA-75% increased from 16 to 32 weeks whereas that of HA-50% was unchanged. HA-50% implants had 100% more bone ingrowth than HA-75% implants after 16 weeks. More HA coating was removed on HA-50% implants compared with HA-75% implants after both 16 and 32 weeks. No further loss of the HA coating was shown from 16 to 32 weeks. Our study suggests that the crystallinity of the HA coating is an important factor in its bioactivity and resorption during weight-bearing conditions. Our findings suggest two phases of coating resorption, an initial rapid loss, followed by a slow loss. Resorbed HA coating was partly replaced by bone ingrowth, suggesting that implant fixation will be durable.

Influence of Post-deposition Heating Time and the Presence of Water Vapor on Sputter-coated Calcium Phosphate Crystallinity

“…Extensive in vitro and in vivo research suggested that CaP coatings are essential for early bone performance when compared with Ti implants (Overgaard et al, 1997(Overgaard et al, , 1999Ong et al, 1998Ong et al, , 2002Ferraz et al, 1999;Blokhuis et al, 2000;Moroni et al, 2002;ter Brugge and Jansen, 2002). Previous characterizations indicated that as-sputtered coatings were amorphous (Ong et al, 1992) but displayed an HA-type crystalline structure after heat treatments (Ong and Lucas, 1994).…”

Biomedical materials and techniques to improve the tribological, mechanical and biomedical properties of orthopedic implants – A review article

“…After 32 weeks, both crystallinity have the same bonding strength with bones -the bonding of 75% crystallinity HA increased and 50% remains the same. However, the low crystallinity induced higher degree of cell growth, Figure 31 shows the bone growth on 50% and 75% crystallinity HA [76]. The arrow shows the HA layer at the interface indicating that higher bone growth was on 50% crystallinity.…”

Preparation of Novel Hydroxyapatite/Yttria‐Stabilized‐Zirconia Gradient Coatings by Magnetron Sputtering

“…It has been reported that both the resistant dissolving capacity of an amorphous HA coating and its stability in a body-fluid environment are lower than those of a crystalline one. [24][25][26][27][28][29] If such an amorphous HA coating were implanted into the human body directly, then it would be invalidated in a short period and fail to satisfy clinical requirements. Therefore, a post-annealing treatment was performed on the gradient coating with water vapor to convert the amorphous coating to a crystalline one.…”